(a) What is the rotational energy of a planet about its spin axis? The radius of the planet is 6140 km, its mass is 6.55 1024 kg, and it has a rotational period of 24.0 h. Treat the planet as a sphere of moment of inertia 2/5 MR2.

(b) Suppose the rotational kinetic energy of the planet is decreasing steadily because of tidal friction. Calculate the change in one day, given that the rotational period of 24.0 h decreases by about 11 µs each year. (Let 1 yr = 365 d).

(b) Suppose the rotational kinetic energy of the planet is decreasing steadily because of tidal friction. Calculate the change in one day, given that the rotational period of 24.0 h decreases by about 11 µs each year. (Let 1 yr = 365 d).

## This question was asked on Mar 17, 2010.

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